Characterisation of Aujeszky's disease viruses isolated from domestic animals and from a wild boar (Sus scrofa) in Italy between 1972 and 1995

Pseudorabies Virus Associations in Wild Animals: Review of Potential Reservoirs for Cross-Host Transmission

Pseudorabies virus (PRV) has received widespread attention for its potential health effects on humans, wildlife, domestic animals, and livestock. In this review, we focus on PRV dynamics in wildlife, given the importance of wild-origin PRV transmission to domestic and farm animals. Wild boars, pigs, and raccoons can serve as reservoirs of PRV, with viral transmission to domestic livestock occurring via several routes, such as wild herd exposure, contaminated meat consumption, and insect vector transmission. Many endangered feline and canine species can be infected with PRV, with acute disease and death within 48 h. The first confirmed human case of PRV infection in mainland China was reported in 2017. Thus, PRV exhibits potentially dangerous cross-host transmission, which is likely associated with inappropriate vaccination, poor awareness, and insufficient biosecurity. Currently, no vaccine provides full protection against PRV in all animals. Here, we summarize the epidemiology and pathogenesis of PRV infection in wild, domestic, and farmed animals, which may facilitate the design of novel therapeutics and strategies for controlling PRV infection and improving wildlife protection in China.

Isolation and molecular characterization of a variant of Chinese gC-genotype II pseudorabies virus from a hunting dog infected by biting a wild boar in Japan and its pathogenicity in a mouse model

We isolated a variant of Chinese pseudorabies virus from a hunting dog with symptoms similar to Aujeszky's disease and designated the isolate MY-1 strain. The dog developed symptoms 6 days after hunting and biting a wild boar and died the day after onset. The Bam HI restriction profile of MY-1 DNA was different from those of the Japanese reference strain Yamagata-S81 and two vaccine strains, Bartha and Begonia, and resembled Bam HI-RFLP (restriction fragment length polymorphism) type IV. Complete nucleotide sequences were determined, and phylogenetic analyses revealed that MY-1 belonged to the same cluster of old Chinese strains and variant strains isolated recently in China, but most of the open reading frames of MY-1 were located on a different branch from those of these Chinese strains. Based on a gC phylogenetic analysis, MY-1 belonged to gC-genotype II composed of those Chinese strains. In mice, the 50% lethal dose (LD₅₀) of MY-1 (10^3.0 TCID₅₀) was almost the same as those of Yamagata-S81 and Bartha. The LD₅₀ value of Begonia was 10^≥4.5 TCID₅₀. The mean survival periods of mice after infection with 10⁴ TCID₅₀ of MY-1, Yamagata-S81 and Bartha were 3.9 days, 2.3 days, and 8.0 days, respectively. The results suggested that the variant of Chinese PRV with slightly weaker pathogenicity than that of wild virulent viruses might be maintained in wild boars in Japan. Furthermore, we would like to propose that old Chinese strains, recent Chinese variant strains, and MY-1 should be grouped as an Asian type PRV.

Evidence of Aujeszky's disease in wild boar in Serbia

BACKGROUND

Aujeszky's disease is a viral disease of suids caused by Suid Herpesvirus 1. The disease has worldwide distribution with significant economic impact. In Serbia, there is neither an Aujeszky's disease eradication nor national vaccination programme of domestic pigs. Since clinical symptoms of Aujeszky's disease are not specific, it is important to establish a link between clinical signs and presence of ADV active infection in wild boars. The aim of this study was to investigate the possibility of active infection within wild boar showing signs of ADV and also to examine relationship between isolates from domestic pigs and wild boar. Having in mind that virus has not been previously isolated from wild boars in Serbia, we report the first isolation of Suid Herpesvirus 1 from this species in Serbia.

RESULTS

Tissue and serum samples from 40 wild boars from eastern Serbia were examined for evidence of Aujeszky's disease (AD). Suid Herpesvirus 1 (SHV1), the cause of AD was isolated on PK15 cell line from three tissue samples, inducing cytopathic effect (CPE) with syncytia forming, and viral genome was detected by polymerase chain reaction (PCR) in eight samples. Genetic analysis of us4, us9 and ul49.5 partial sequences showed high homology between ADV isolates from wild boars and between isolates from wild boars and domestic animals. Neutralizing antibodies were not detected by virus neutralisation test (VNT) in sera from four out of eight PCR positive wild boars suggesting recent infection in those animals.

CONCLUSIONS

This is the first demonstration of Aujeszky's disease virus (ADV) in the wild boar population in Serbia although seroconversion has been detected previously.

Age- and strain-dependent differences in the outcome of experimental infections of domestic pigs with wild boar pseudorabies virus isolates

Although pseudorabies virus (PRV) has been eradicated in domestic swine in many countries, its presence in wild boars remains a threat for a reintroduction into the currently unprotected swine population. To assess the possible impact of such a reintroduction in a naive herd, an in vivo infection study using two genetically characterized wild boar PRV isolates (BEL24043 and BEL20075) representative for wild boar strains circulating in south-western and central Europe and the virulent NIA3 reference strain was performed in 2- and 15-week-old domestic pigs. Our study revealed an attenuated nature of both wild boar strains in 15-week-old pigs. In contrast, it showed the capacity of strain BEL24043 to induce severe clinical symptoms and mortality in young piglets, thereby confirming that the known age dependency of disease outcome after PRV infection also holds for wild boar isolates. Despite the absence of clinical disease in 15-week-old sows, both wild boar PRV strains were able to induce seroconversion, but to a different extent. Importantly, differences in infection and transmission capacity of both strains were observed in 15-week-old sows. Strain BEL24043 induced a more prolonged and disseminated infection than strain BEL20075 and was able to spread efficiently to contact animals, indicative of its capacity to induce a sustained infection. In conclusion, it was shown that a reintroduction of a wild boar isolate into the domestic swine population could have serious economic consequences due to the induction of clinical symptoms in piglets and by jeopardizing the PRV-negative status.

Detection and molecular analysis of Pseudorabies virus strains isolated from dogs and a wild boar in Italy

Aujeszky's disease (AD) is one of the most economically important diseases of farmed pigs. Wild boars can act as reservoirs and might represent a potential threat for domestic animals, including dogs. The aim of this study was to report the results of an AD survey based on the Pseudorabies virus (PRV) genome detection in samples of dogs clinically suspected of AD and of wild boars collected during four consecutive hunting seasons in the period 2010-2014. Genomic characterization was based on the partial gC sequence of the Italian strains and the comparison with those from domestic pigs and European PRV strains circulating in wild boars. The Italian PRV strains were mainly distributed into three different clusters and revealed two interesting findings. First, there was a clear distinction between the viral strains that were isolated from dogs used for hunting and subsequently traced back to wild boars and the strains that were isolated from working dogs and subsequently found to be closely related to domestic pigs. Second, the Italian epidemiological situation was found to be different from those of European countries in that the Italian situation was characterized by the presence of both the typical Italian clades 1 and 2 and supported by new patterns of aa deletions/insertions. Italian clade 1 included strains from hunting dogs and two Italian wild boars, and Italian clade 2 grouped with recent strains from dogs that were unable to hunt and domestic pigs that were related to one old reference strain (S66) and not included elsewhere. Molecular and phylogenetic analyses of PRV strains are therefore necessary to improve the understanding of the distribution of the PRV clusters and their evolution.

Serologic, molecular, and pathologic survey of pseudorabies virus infection in hunted wild boars (Sus scrofa) in Italy

To investigate pseudorabies-virus (PrV) -antibody and viral-DNA prevalence, we collected blood, nasal and genital swabs, and tonsillar and lymph-node tissue samples from 139 wild boars (Sus scrofa; 39 piglets, 30 juveniles, and 70 adults), during the hunting season of 2010-2011 in Tuscany, Central Italy. We performed immunohistochemistry with anti-PrV monoclonal antibodies on selected tissue samples. Forty-three of 139 (30.9%) boars were PrV-antibody positive and a 1,954-base-pair PrV-specific product was amplified from nine nasal (6.5%) and 26 genital (18.7%) swabs. Sequence analysis of PrV-positive PCR products revealed identity scores of 99-100% with Suid herpesvirus 1 strain Becker (JF797219) and confirmed the identification of PrV DNA in tested swabs. There was significantly higher antibody prevalence in adults than in juveniles and in piglets than in juveniles. The prevalence of viral DNA was significantly higher in genital swabs than in nasal specimens. The percentage of positive nasal swabs did not differ among age classes. Piglets had a higher percentage of PCR-positive genital swabs than juvenile and adult subjects (30.8% vs. 13.3% and 14.3%, respectively). Results confirmed that PrV infection is widespread in the wild boar population in the study area. The presence of anti-PrV antibodies and of the PrV virus in piglets could be related to vertical transmission of the virus. This hypothesis was also supported by a higher presence of viral genome in genital swabs than in nasal swabs. This field study supports the importance of vertical transmission of PrV, and the high prevalence of virus in genital swabs supports venereal transmission in adult feral boars.

Molecular characterization of Belgian pseudorabies virus isolates from domestic swine and wild boar

Aujeszky's disease is an economically important disease in domestic swine caused by suid herpesvirus 1, also called pseudorabies virus (PRV). In several European countries, including Belgium, the virus has successfully been eradicated from the domestic swine population. The presence of PRV in the wild boar population however poses a risk for possible reintroduction of the virus into the domestic pig population. It is therefore important to assess the genetic relatedness between circulating strains and possible epidemiological links. In this study, nine historical Belgian domestic swine isolates that circulated before 1990 and five recent wild boar isolates obtained since 2006 from Belgium and the Grand Duchy of Luxembourg were genetically characterized by restriction fragment length polymorphism (RFLP) analysis and phylogenetic analysis. While all wild boar isolates were characterized as type I RFLP genotypes, the RFLP patterns of the domestic swine isolates suggest that a shift from genotype I to genotype II might have occurred in the 1980s in the domestic population. By phylogenetic analysis, Belgian wild boar isolates belonging to both clade A and B were observed, while all domestic swine isolates clustered within clade A. The joint phylogenetic analysis of both wild boar and domestic swine strains showed that some isolates with identical sequences were present within both populations, raising the question whether these strains represent an increased risk for reintroduction of the virus into the domestic population.

Pseudorabies virus in wild swine: a global perspective

Suid herpesvirus 1 (SuHV1, syn. Aujeszky's disease virus [ADV] or pseudorabies virus [PrV]), which belongs to the family Herpesviridae, subfamily Alphaherpesvirinae, genus Varicellovirus is the causative agent of Aujeszky's disease (AD, pseudorabies), a notifiable disease, that causes substantial economic losses to the swine industry in countries, where AD is present. Members of the family Suidae (true pigs) are the only natural hosts for PrV, although the virus can infect numerous other mammals including ruminants, carnivores and rodents. Despite the tremendous progress that has been made in controlling and eliminating PrV in domestic pigs, there is mounting evidence that PrV infections are more widespread in wild swine across the world than originally thought. Unfortunately, our understanding of the extent of PrV infections in these wild populations and of the threat to domestic swine is still fragmentary. This review aims at giving a global perspective on PrV infections in wild swine by scrutinizing the current state of knowledge concerning (i) the global occurrence of PrV infections in free-living populations of wild swine, e.g., wild boar and feral swine, (ii) the molecular characterization of wild swine PrV, (iii) infection characteristics of PrV in populations of wild swine, (iv) the risk of spillover infections to domestic pigs, (v) potential risk-mitigating measures, focusing on further research needs.

Characterization of pseudorabies virus of wild boar origin from Europe

Pseudorabies virus (PrV) infections appear to be more widely distributed in the European wild boar (Sus scrofa) population than assumed. In Europe, attempts to isolate and characterize the causative agents have been limited so far. We therefore collected and examined a total of 35 PrV isolates obtained from wild boar or hunting dogs in Germany, France, Spain, Italy, Slovakia and Hungary between 1993 and 2008. Restriction enzyme analysis of genomic DNA using BamHI showed that all isolates, except one, belonged to genogroup I but different subtypes were evident. For further investigations of the phylogenetic relationships, a 732-bp fragment of the glycoprotein C (gC) gene was amplified by PCR. Sequence analysis revealed about 40 variant positions within this fragment. Comparison of the nucleotide sequences supported the separation into a clade containing isolates from North-Rhine Westphalia, Rhineland-Palatinate (Germany), France and Spain (clade B) and an apparently more variable clade comprising isolates from Brandenburg, Baden-Wurttemberg, Saxony, Saxony-Anhalt (Germany), Slovakia, Hungary, Italy and France (clade A).

A serological survey of selected pathogens in wild boar in Slovenia

Serum samples collected from 178 shot wild boars (Sus scrofa) were tested for the presence of antibodies against classical swine fever virus, Aujeszky's disease virus (ADV), porcine reproductive and respiratory syndrome virus, porcine respiratory coronavirus (PRCV), transmissible gastroenteritis virus, swine influenza virus, porcine parvovirus (PPV), swine vesicular disease virus, Actinobacillus pleuropneumoniae (APP), Mycoplasma hyopneumoniae, Salmonella spp., Brucella spp. and Haemophilus parasuis (HPS) throughout Slovenia during the hunting season 2003/2004. The number of samples corresponds to 3% of the total hunting bag. By enzyme‐linked immunosorbent assay (ELISA) antibodies against ADV were detected in 55 sera (31%), against PRCV in five sera (3%), PPV in 87 sera (49%), APP in 93 sera (52%), M. hyopneumoniae in 38 sera (21%), Salmonella spp. in 85 sera (47%) and HPS in 33 sera (18%).

Caracterização antigênica e molecular de oito amostras do vírus da doença de Aujeszky isoladas no estado do Rio Grande do Sul em 2003

A doença de Aujeszky ou pseudoraiva (DA), causada pelo vírus da pseudoraiva (PRV) é a maior preocupação na produção de suínos. No estado do Rio Grande do Sul, Brasil, a DA foi somente detectada em 1954, em bovino. Em 2003, ocorreram dois surtos de encefalite em granjas na região norte do estado, fronteira com o estado de Santa Catarina. O vírus da doença de Aujeszky (VDA) foi isolado a partir de animais coletados em oito granjas distintas da região e submetido a análises antigênicas e moleculares. As amostras de VDA isoladas foram comparadas com as amostras padrão NIA-3 e NP. A caracterização antigênica dos mesmos foi realizada com testes de imunoperoxidase frente a um painel de anticorpos mono-clonais (Mabs) preparado contra epitopos de glicoproteinas virais (gB, gC, gD e gE). A caracterização genômica foi realizada através da análise restrição enzimática (REA) sobre o genoma total das amostras, com a enzima de restrição (REA) Bam HI. O perfil antigênico das oito amostras isoladas no Rio Grande do Sul, bem como os apresentados pelas amostras padrão NIA-3 e NP, foram similares. A REA revelou que todos as oito amostras do Rio Grande do Sul apresentaram um arranjo genômico do tipo II, genótipo frequentemente encontrado em surtos prévios de DA em outros estados do Brasil. Os resultados aqui obtidos indicam que as oito amostras isoladas no Rio Grande do Sul são similares.

Prevalence of antibodies to classical swine fever, Aujeszky's disease, porcine reproductive and respiratory syndrome, and bovine viral diarrhoea viruses in wild boars in Croatia

During the hunting season in February 1999, a total of 44 blood samples were collected from wild boars shot in the area of Moslavacka gora. These blood samples were examined by enzyme immunoassay for the presence of antibodies to classical swine fever (CSFV), Aujeszky's disease (ADV), bovine viral diarrhoea (BVDV), and porcine reproductive and respiratory syndrome (PRRSV) viruses. Out of 44 serum samples examined, 17 (38.63%) were positive for CSFV, 24 (54.54%) were positive for ADV and two (4.54%) were positive for BVDV. All sera were negative for PRRSV. The results, recorded for the first time in Croatia, supported the hypothesis that wild boar act as a potential reservoir of CSFV, ADV and BVDV, and thus have a role in the epidemiology of these diseases.

Characterization of the DNA polymerase loci of the novel porcine lymphotropic herpesviruses 1 and 2 in domestic and feral pigs

Two novel porcine gammaherpesviruses, porcine lymphotropic herpesviruses 1 and 2 (PLHV-1 and -2), have been detected by amplification of short DNA polymerase (DPOL) sequences from blood and spleen of domestic pigs while searching for unknown herpesviruses in pigs as possible risk factors in xenotransplantation. In the present study, the DPOL genes of the two viruses and the open reading frames (ORFs) that follow in the downstream direction were amplified by PCR-based genome walking from adaptor-ligated restriction fragment libraries of porcine spleen samples. The sequences determined for the two PLHVs exhibited a very low G+C content (37 mol%) and a marked suppression of the CpG dinucleotide frequency. The DPOL proteins encoded were 95% identical and showed a close relationship (60% identity) to the DPOL protein of a ruminant gammaherpesvirus, alcelaphine herpesvirus 1 (AlHV-1). This was confirmed by phylogenetic analyses of the conserved regions of the two PLHV DPOL proteins. The PLHV ORFs downstream of DPOL exhibited 83% identity to each other and >>50% similarity to ORF A5, the position equivalent of AlHV-1. From these data, the PLHVs can be firmly classified to the subfamily Gammaherpesvirinae: To find a natural reservoir for the PLHVs, organs of feral pigs were screened with five different PCR assays, targetting either the DPOL gene or 3'-flanking sequences. In all samples, PLHV sequences were detected that originated predominantly from PLHV-2, suggesting the possibility of virus transfer between feral and domestic pig populations.